Not Downstream of Major/Multiple Dams and Reservoirs
Summit & Grand counties have a number of dams. Many of them, if they
failed, would produce catastrophic damage and probable loss of human
life. If/When you move here, keep this in mind. There are plenty of
great areas to live that are not in the flood path of failing dams. The
dams are a PLUS to the community in that they provide or have the
potential to provide power to the counties which does not depend on
outside sources. Some hazards you just have to learn to live with. In
any case, the potential for failure has been determined to be LOW in
both counties.
Grand County
Grand County Pre-Disaster Mitigation Plan (Download
PDF)
Grand County is home to a number of dams, damage to which could prove to
be severely disruptive and even deadly to county residents, as well as
others. For example, failure of Granby Dam would inundate I-70, US 6 and
US24 from DeBeque to Palisade in Mesa County.
Class I and Class II dams are defined as follows:
CLASS I:
A dam which, having failed, would result in
probable loss of human life.
CLASS II:
Significant damage is expected, but not loss
of human life.
Grand County has 9 Class I and 9 Class II dams.
The Class I hazard dams all have
emergency action plans.
Summit County
Summit County Multi-Hazard Mitigation Plan (Download
PDF)
Dam Failure
Hazard Description
Dams are manmade structures built for a variety of uses, including flood
protection, power, agriculture, water supply, and recreation. Dams
typically are constructed of earth, rock, concrete, or mine tailings.
Two factors that influence the potential severity of a full or partial
dam failure are the amount of water impounded and the density, type, and
value of development and infrastructure located downstream.
Dam failures can result from any one or a combination of the following
causes:
• Prolonged periods of rainfall and flooding, which result in
overtopping (overtopping is the primary cause of earthen dam failure)
• Earthquake
• Inadequate spillway capacity resulting in excess overtopping flows
• Internal erosion caused by embankment or foundation leakage or piping
or rodent activity
• Improper design
• Improper maintenance
• Negligent operation
• Failure of upstream dams on the same waterway
Geographic Location
The geographic extent of this hazard in Summit County is small—10-25
percent of the planning area affected.
HAZUS-MH contains a database of dams based on
the National Inventory of Dams. This database lists nine dams in the
County and classifies dams based on the potential hazard to the
downstream area resulting from failure or mis-operation of the dam or
facilities:
• High Hazard Potential—Probable loss of life
(one or more)
• Significant Hazard Potential—No probable
loss of human life but can cause economic loss, environment damage,
disruption of lifeline facilities, or impact other concerns; often
located in predominantly rural or agricultural areas but could be
located in areas with population and significant infrastructure
• Low Hazard Potential—No probable loss of
human life and low economic and/or environmental losses; losses are
principally limited to the owner’s property Based on these
classifications, there are five high hazard dams, two significant hazard
dams, and two low hazard dams in Summit County. These dams are listed in
Table 3.4.
The high and significant hazard dams all have emergency action plans.
Risk to dam failure is greatest to the Town of Silverthorne immediately
downstream of the Dillon dam. Breckenridge could be impacted by a
failure of the Goose Pasture Tarn dam. Unincorporated areas downstream
of all high hazard dams are at risk if a failure occurred. There is
little risk to Blue River, Montezuma, or the Town of Dillon.
Previous Occurrences
There was no information available indicating that dam failures had
occurred in Summit County in the past.
Probability of Future Occurrence
Unlikely—Less than 1 percent chance of
occurrence in next 100 years or has a recurrence interval of greater
than every 100 years.
Using the methodology adopted for natural hazards in this plan, no past
events represent an unlikely probability of future occurrence. However,
because dam failure is a manmade hazard, the methodology for calculating
probability based on past occurrences does not necessarily reflect the
actual risk of future occurrence. Further information on this risk is
unknown.
Magnitude/Severity
Catastrophic—Multiple deaths; property
destroyed and severely damaged; and/or interruption of essential
facilities and service for more than 72 hours.
Water released by a failed dam generates tremendous energy and can cause
a flood that is catastrophic to life and property located in the
inundation area. Of particular concern is the Green Mountain Dam, where
exposure conditions at the dam site are very harsh, with many cycles of
freezing and thawing and large temperature swings, particularly on
south-facing slopes. In 1998, the Bureau of Reclamation, the agency that
manages the dam, conducted a condition assessment of the spillway. It
determined that overall the spillway was in good condition. However,
there were a number of areas that needed repair. Some of the previous
repairs had failed and needed to
be replaced.
The Criteria List - How the 2 Counties
Stack Up (follow links to detailed information)
Membership Goals:
Our target goals for voting age self-reliant survivalist members:
Grand County: 13,406 population x 15% = 2,011 members
Summit County: 28,296 population x 15% = 4,245 members
Total voting age members wanted: 6,256,
although half that would make a BIG difference to the counties.
If you already live in Summit or Grand Counties,
contact MEG to let us know!
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